In the field of radio communication, and mobile communication in particular, a variety of information such as image and data in addition to voice is becoming transmission targets in recent years. Since it is anticipated that the demand for transmission of various contents will increase at an accelerated pace in the future, the necessity for more reliable and faster transmission will further increase. However, when high-speed transmission is carried out in a mobile communication, influences of multipath delay signals cannot be ignored and the transmission characteristic deteriorates due to frequency selective fading.
As one of technologies for handling frequency selective fading, a multicarrier (MC) modulation scheme such as an OFDM (Orthogonal Frequency Division Multiplexing) scheme is becoming a focus of attention. The multicarrier modulation scheme is a technology for realizing high-speed transmission as a result of transmitting data using a plurality of carriers (subcarriers) whose transmission rate is suppressed to an extent that frequency selective fading is not generated. Especially, because a plurality of subcarriers on which data is arranged is orthogonal to one another, the OFDM scheme is a scheme with the highest frequency utilization efficiency among multicarrier modulation schemes and it can be implemented in a relatively simple hardware configuration, and therefore the OFDM scheme is capturing special attention and is now under study from various angles.
As an example of such studies, there is an OFDM scheme which exercises control so as to avoid transmitting subcarriers of low reception quality in anticipation that the peak value (peak power) of transmit power will decrease. Furthermore, in exercising this control, it tries to minimize the deterioration of a BER (Bit Error Rate) by making bits assigned to subcarriers not to be transmitted coincide with bits to be punctured (e.g., see “Performance of the Delay Profile Information Channel based Subcarrier Transmit Power Control Technique for OFDM/FDD Systems” (Noriyuki MAEDA, Seiichi SAMPEI, and Norihiko MORINAGA, transactions of Institute of Electronics, Information and Communication Engineers, B, Vol. J84-B, No. 2, pp. 205-213 (February 2001)).
However, there is a possibility in the above described method that when there are subcarriers not to be transmitted, the number of bits that can be transmitted may be decreased and the error rate characteristic may deteriorate a great deal. Furthermore, it is necessary to transmit position information on the subcarriers not to be transmitted from a base station to mobile stations separately, which reduces the transmission efficiency. Moreover, simply exercising control so as to avoid transmission of subcarriers of low reception quality may contrarily increase peak power depending on a phase relationship between QPSK-modulated subcarriers, etc.